1. Field of the Invention
The present invention relates to an image reading apparatus, an image forming apparatus, an image reading method, an image forming method, and a computer program product.
2. Description of the Related Art
Some image reading apparatuses are provided with an auto document feeder (ADF) to feed originals one by one to a scanner unit. FIG. 12 is a schematic diagram of an internal structure of a conventional image reading apparatus provided with an ADF. The conventional image reading apparatus includes a scanner 210, and an ADF 230 located above the scanner 210.
A stack of originals (not shown) is set on an original tray 241 of the ADF 230 and originals picked up one by one by a pickup roller 242. The picked-up original is fed in an arrow PA direction to pass through between a pair of registration rollers 243. The original then passes along a glass plate 240 in an arrow PC direction (which is a sub-scanning direction, a feeding direction, or a plus (+) y direction) by pressing rollers 245 arranged along a feed path of an outer peripheral portion of a feed drum (platen) 244 that is made to rotate in an arrow PB direction and by the feed drum 244. The original is scanned in an x direction (main scanning direction) while it passes along the glass plate 240, and the original is ejected by paper ejection rollers 246 and 247 in an arrow PD direction to be placed on a paper ejection tray 248.
Meanwhile, the scanner 210 includes a contact glass 231, the glass plate 240, a first carriage 253 as a scanning unit, a second carriage 254 as a reflecting unit, a lens 236, a charge-coupled device (CCD) 207, and a carriage motor (stepping motor) 238.
The first carriage 253 includes a lamp (halogen lamp) 232 and a mirror 233 inside thereof. Light emitted from the lamp 232, which lights up only upon reading (scanning) the original, passes through the glass plate 240. The light having passed therethrough is irradiated to one line of the original on the feed drum 244 in the main scanning direction, is reflected by the original, and again passes through the glass plate 240. A position of an optical path L1, where the light reflected from the feed drum 244 passes through the glass plate 240 and enters the mirror 233, is set as a reading position.
The light having passed through the glass plate 240 is bent by mirrors 234 and 235 in the second carriage 254 along U-shape optical paths L2 to L4, is collected by the lens 236 to be photoelectrically converted by the CCD 207, and is output as image data.
The first carriage 253 and the second carriage 254 can move in the +y direction by rotational driving of the carriage motor 238. Positions of the first carriage 253 and the second carriage 254 at home positions (HP) are indicated by solid lines in FIG. 12, and positions of the first carriage 253 and the second carriage 254 at maximum scanning positions are indicated by dashed two-dotted lines therein. When reading the original while it is fed by the feed drum 244, the first carriage 253 is located at the home position (HP). When reading the original not fed thereby but fixed on the contact glass 231, the first carriage 253 moves along an image scanning area (maximum length) by setting a position as another home position that is apart from the home position (HP) by “c” explained later.
When a large number of originals are read using the ADF 230 and if a buffer memory becomes full, for example, this type of image reading apparatus cannot store image data any more. Therefore, even when an original is in the middle of being read, the reading operation of the image data for the original is interrupted (hereinafter, “intermission”).
When intermission occurs in the ADF 230, reading by the CCD 207 can be instantly stopped, but the feed drum 244 cannot quickly stop because the feed drum 244 has rotational kinetic energy K (K=Iω2/2, where I is moment of inertia and ω is angular velocity), and thus the feed drum 244 is caused to decelerate and then stop. Besides, when the feed drum 244 is again made to rotate, an angular velocity of the feed drum 244 needs to be increased at an angular acceleration dω/dt until the angular velocity reaches a feed rate or a feed velocity v (v=rω, where r is radius of the feed drum 244) being a steady rate because of the moment of inertia I. Therefore, the original is fed in such a manner that the feed rate of the original is decreased from the steady rate (read rate) due to the inertia and then the original stops after a certain time passes since it is decreased and the feed rate of the original is increased from the stopped state to reach the read rate after a certain time passes since it is increased.
Moreover, when the original is read during changing of an original feed rate, this causes an abnormal image data such as its extension, deformation, and displacement. Therefore, the original is not read while the original feed rate is changing caused by occurrence of the intermission, but the original is read instead while the first carriage is moved in the feeding direction during stopping of the original in the intermission. The movement of the first carriage allows the original to be read only when the original feed rate is stable. Thus, a technology of using the above method to prevent occurrence of the abnormal image caused by the intermission is already known.
FIGS. 13A to 13I are diagrams for explaining positional relationships between the original and the first carriage 253 in the image reading apparatus shown in FIG. 12. FIGS. 14A and 14B are flowchart of how the original is read in an ADF mode in the image reading apparatus in FIG. 12.
FIG. 13A is a conceptual diagram of the positional relationship among the original, the carriage, the home position (HP) being a standby position of the carriage, and reading areas. In FIGS. 13B to 13I, X and Y are coordinates indicating marks on the original for convenience in explanation on movement of the original and movement of the carriage. In FIGS. 13A to 13I, a solid black area of the original indicates image reading areas before and after the intermission, a mesh area thereof indicates a reading area when the original is stopped caused by the intermission, and a white area thereof indicates an area of the original before being read. Although the original is bent in an arc while being fed along the feed drum 244, it is shown flat here for convenience in explanation.
In FIG. 13B, the first carriage 253 is located at the home position (HP) in which the reading position is the standby position.
In FIG. 13C, when a buffer memory (not shown) runs out of its free space and a memory-full signal is generated, the reading operation in the CCD 207 is stopped. However, because the feed drum 244 has the moment of inertia, the original cannot stop instantly, i.e., the original comes to a stop after some time. FIG. 13C shows movement of the original in this case, i.e., the original moves from a position indicated by a dotted line to a position indicated by a solid line within this time. An area for a distance from the position of the original indicated by the dotted line to the position indicated by the solid line is already read by the CCD 207 and is thereby included in the solid black area.
In FIG. 13D, assuming that the original is decelerated to a stop in the distance from the position indicated by the dotted line to the position indicated by the solid line in the +y direction, an area for a deceleration distance from a position (X) on the original when the CCD 207 stops an original reading operation to a position (Y) on the original when the original is actually stopped has not been read because the CCD 207 had stopped the original reading operation. Namely, when the original is stopped, the original is located at the position (Y) that is the reading position (home position) of the first carriage 253.
In FIG. 13E, the first carriage 253 reads an area (intermission area) of the original by the CCD 207 in a period from stopping the original after start of its deceleration to accelerating the original upon restart of reading to reach a rate required for the reading. Specifically, the first carriage 253 reads a mesh area of the original by the CCD 207 from the position (Y) to the position (X) while moving from the reading position in the +y direction by a distance X-Y (intermission reading).
In FIG. 13F, when the CCD 207 finishes the reading of the area between the position (Y) and the position (X) on the original, the first carriage 253 is stopped to enter a standby state.
In FIG. 13G, when the cause of the interruption in the reading of the original is resolved (e.g., when the free space of the memory for storing therein image data is sufficiently freed up), the reading of the original is restarted.
When the reading of the original is restarted, feeding of the original is started from the position indicated by the dotted line. Even if the feeding of the original is started, it takes time until its rate reaches the rate required for reading. However, the reading of the area between the position (X) and the position (Y) is already finished.
In FIG. 13H, because the original is being accelerated in the area from the position indicated by the dotted line to the position indicated by the solid line, the CCD 207 is in a standby state without performing the reading operation.
In FIG. 13I, when the feed rate of the original reaches a rate required to read the original, the CCD 207 restarts the original reading operation and reads an area from the position (Y) of the original indicated as the solid black area.
The reciprocating movement of the first carriage 253 as shown in FIGS. 13A to 13I is further explained with reference to the flowcharts in FIGS. 14A and 14B.
As shown in FIG. 14A, first, the ADF mode is set (Step S51), then the feed drum 244 is made to rotate and starts feeding the original (Step S52), and an image reading operation is started by an instruction of a central processing unit (CPU) 261 as a control unit (Step S53). When the image reading operation is started, the number of times of original reading is set to an n-th time (in this case, n is 1) (Step S54).
When the ADF 230 is reading the original, the CPU 261 determines whether a memory-full signal has been received (Step S55). Specifically, generation of the memory-full signal is the cause of the interruption in the reading operation, and is a signal, instructed by an image-storage controller 273, indicating reduction in the free space of the buffer memory.
When having received the memory-full signal (Yes at Step S55), the ADF 230 interrupts the reading operation at this point in time (Step S56) (see FIG. 14B).
The original is decelerated and comes to a stop (Step S57).
Next, the CCD 207 reads the original by the instruction of the CPU 261 while the first carriage 253 moves from the position where the original is decelerated to a stop to the position where the CCD 207 stops the original reading operation (Step S58).
The first carriage 253 reaches the position (X) of the original and stands by thereat (Step S59) by the instruction of the CPU 261, and the CPU 261 determines whether a memory-empty signal has been received (Step S60). At this time, the first carriage 253 is located at the position (X) where the CCD 207 stops the original reading operation.
When the factor to interrupt the reading of the original is resolved (when the memory space that stores image data is sufficiently freed up), the image-storage controller 273 issues the memory-empty signal. When having received the memory-empty signal (Yes at Step S60), the CPU 261 restarts the original feeding (Step S61).
When the original feeding is restarted, the CCD 207 restarts reading the original upon reaching the read rate of the original, and reads the area which has not been read.
At this time, “n” at Step S63 becomes 2 (2 is obtained by substituting 1 for n of “n+1” in the right-hand side), and process returns to Step S54.
Thereafter, it is determined at Step S55 whether the memory-full signal has been received.
It is noted that when the image reading apparatus does not receive the memory-full signal and finishes the reading operation of a sheet of original (normal reading), the number n of times of the original reading is 1. When the image reading apparatus receives the memory-full signal, temporarily interrupts the reading operation of a sheet of original, and restarts it (intermission reading), then the number n of times of the original reading becomes at least 2.
When the memory-full signal has not been received (No at Step S55), the CPU 261 determines whether the original has been read to a trailing edge thereof (Step S64). When the original has not been read to the trailing edge (No at Step S64), process returns to Step S54, while when the original has been read to the trailing edge (Yes at Step S64), the CPU 261 ends the image reading (Step S65), ejects the original from the ADF 230, and ends the process (Step S66).
FIG. 15 is a schematic for explaining a positional relationship between the feed drum 244 and the first carriage 253 of the image reading apparatus shown in FIG. 12.
According to the image reading method as shown in FIGS. 13A to 13I and FIG. 14, when the CPU 261 does not receive the memory-full signal from the image-storage controller 273 during the original reading operation, the first carriage 253 stands by at the home position (HP) (number n of times of the original reading: n=1).
However, when the CPU 261 receives the memory-full signal from the image-storage controller 273 during the original reading operation and interrupts the original reading, the first carriage 253 moves in the +y direction by an area of a first intermission (which corresponds to the area between the position (X) and the position (Y) in FIG. 13A), and enters standby.
When the CPU 261 receives again the memory-full signal therefrom during the reading operation of a next original and interrupts the original reading, the first carriage 253 moves up to a position of a second intermission from the position of the first intermission in the +y direction, and enters standby.
When the CPU 261 receives again the memory-full signal therefrom during the reading operation of a further next original and interrupts the original reading, the first carriage 253 moves up to a position of a third intermission from the position of the second intermission in the +y direction, and enters standby.
Thereafter, when the CPU 261 receives again the memory-full signal during the reading operation of an original and interrupts the original reading, the first carriage 253 moves by a distance for one intermission in the +y direction, and eventually, the first carriage 253 is off the glass plate 240 which is a readable area, so that the original cannot be read.
A factor by which the original cannot be read is because the first carriage 253 is caused to move in the feeding direction (+y direction) each time the intermission occurs and then stand by at the position as it is, as shown in FIGS. 13B to 13I and Steps S54 to S63 in FIG. 14.
Therefore, to solve the problem on displacement of the first carriage 253 from the glass plate 240, a technology as follows has been proposed. That is, as shown in FIGS. 16A to 16I, the reading operation is performed while the first carriage 253 is moved in the feeding direction, and then, the first carriage 253 is returned to the home position (HP).
FIGS. 16A to 16I are diagrams for explaining a relationship between the original and the first carriage in the image reading apparatus according to the present invention.
FIGS. 16A to 16E are the same as FIGS. 13B to 13F, and therefore explanation thereof is omitted hereinafter.
In FIG. 16F, the first carriage 253 is returned to the home position (HP).
In FIG. 16G, when the feeding of the original is restarted, the original is accelerated to a rate required for reading.
In FIG. 16H, the acceleration of the original is completed.
In FIG. 16I, the original enters a constant-rate state, and the CCD 207 restarts to read the original.
As explained above, in the technology using the method of returning the first carriage 253 to the home position (HP) as shown in FIGS. 16A to 16I, if the CCD 207 reads the original in the area where the original is being accelerated, the image data is deformed, and thus, the reading operation is stopped in this area. Therefore, the image data near an intermission portion is scanned only from the deceleration area (intermission reading), which causes the image data to become discontinuous.
Meanwhile, Japanese Patent No. 3701621 discloses another conventional technology. The disclosed technology is achieved to prevent occurrence of an abnormal image caused by intermission of an ADF by not reading an original during deceleration or acceleration of the original, but by reading image data, instead, simultaneously when a carriage is moved during stop of the original due to the intermission of the ADF, and by putting image data before and after the intermission together with image data during the intermission, so that the original is read only when the feed rate of the original is stable. The disclosed technology, however, has a problem that repetition of intermission causes the carriage to move, to be off from a glass plate which is a readable area, and to become incapable of reading the original.